In vivo measurements of airway geometry and their mechanical properties are of fundamental use in pulmonary physiology and of clinical use in the assessment of lung airway disease, both for initial screening and for differential diagnosis. Radiographic bronchograms can be tediously analyzed to obtain dimensions of the airways. However, this proposal makes use of a rapid non-invasive technique, an acoustic impulse response from the airways, to obtain a measure of the input impedance over a frequency range that has been shown under the existing grant to contain information about airway geometry, including peripheral airways. An acoustic pressure pulse is applied as a barely noticeable input at the airway opening. The reflected pressure wave is recorded in time, and analysis of this wave and the incident wave results in an estimation of the frequency responses of the input impedance over the frequency range 100 to 10 to the 4th power Hz. These data are then analyzed using data inversion methods to obtain the serial distribution of airway properties. The airway property of primary interest is the total cross-sectional area. The present proposal is thus to apply the acoustic impulse response technique, to implement data inversion methods to estimate the serial distribution of airway geometry, and to test these against direct measurements in order to assess their accuracy and limits of usefulness in vivo.